Retuning of ferroelectric media built-in-bias

Abstract

Provided herein are embodiments for adjusting a built-in bias of a media including a conductive layer and a ferroelectric layer above the conductive layer. In certain embodiments, a voltage signal is applied between the conductive layer of the media and an electrode (provided over at least a portion of the ferroelectric layer) to thereby tune the built-in bias so that the built-in bias moves in a direction of (i.e., towards) the desired built-in bias. In other embodiments, the temperature of the at least a portion of the ferroelectric layer of the media is elevated to thereby tune the built-in bias so that the built-in bias moves in a direction of (i.e., towards) the desired built-in bias. The desired built-in bias can be a zero built-in bias, or a non-zero built-in bias.

1 . A method for adjusting a built-in bias of a media including a conductive layer and a ferroelectric layer above the conductive layer, the method comprising:
 (a) providing an electrode over at least a portion of the ferroelectric layer of the media;   (b) using the electrode to measure the built-in bias of the portion of the media over which the electrode is provided, wherein the built-in bias causes a preference for polarization in one of two directions that are opposite one another;   (c) comparing the measured built-in bias to a desired built-in bias; and   (d) applying a voltage signal between the conductive layer of the media and the electrode to thereby tune the built-in bias so that the built-in bias moves in a direction of the desired built-in bias.   
   
   
       2 . The method of  claim 1 , wherein:
 the two directions comprise an up direction and a down direction; and   the voltage signal applied at step (d) toggles between a positive voltage level and a negative voltage level, the positive voltage level being sufficient to change the polarization of the ferroelectric layer of the media from an up direction polarization to a down direction polarization, and the negative voltage level being sufficient to change the polarization of the ferroelectric layer of the media from a down direction polarization to an up direction polarization.   
   
   
       3 . The method of  claim 1 , wherein the voltage signal applied at step (d) causes repeated switching of the polarization of the portion of the ferroelectric layer of the media over which the electrode is provided. 
   
   
       4 . The method of  claim 1 , wherein step (d) comprises only applying the voltage signal if the built-in bias measured at step (b) is not within a specified tolerance of the desired built-in bias. 
   
   
       5 . The method of  claim 4 , wherein steps (b), (c) and (d) are repeated until the measured built-in bias is within the specified tolerance of the desired built-in bias, and wherein each time the built-in bias is measured at step (b) the voltage signal is unapplied so that the voltage signal does not affect measurement of the built-in bias. 
   
   
       6 . The method of  claim 5 , further comprising:
 (e) removing the electrode after the built-in bias is within the specified tolerance of the desired built-in bias.   
   
   
       7 - 15 . (canceled) 
   
   
       16 . A method for adjusting the built-in bias of media including a conductive layer and a ferroelectric layer above the conductive layer, the method comprising:
 (a) providing an electrode over a portion of the ferroelectric layer of the media; and   (b) applying a voltage signal between the conductive layer of the media and the electrode to thereby repeatedly switch a polarization of the portion ferroelectric layer of the media over which the electrode is provided, in order to thereby reduce a magnitude of the built-in bias;   wherein steps (a) and (b) are performed before user data is written to the portion of the media over which the electrode is provided.   
   
   
       17 . The method of  claim 16 , wherein step (b) comprises repeatedly switching between an up polarization and a down polarization. 
   
   
       18 - 20 . (canceled) 
   
   
       21 . A method for adjusting a built-in bias of a media including a conductive layer and a ferroelectric layer above the conductive layer, the method comprising:
 (a) measuring the built-in bias of at least a portion of the media, wherein the built-in bias causes a preference for polarization in one of two directions that are opposite one another;   (b) comparing the measured built-in bias to a desired built-in bias; and   (c) elevating the temperature of the at least a portion of the ferroelectric layer of the media to thereby tune the built-in bias so that the built-in bias moves in a direction of the desired built-in bias.   
   
   
       22 . The method of  claim 21 , wherein step (c) comprises elevating the temperature of the at least a portion of the ferroelectric layer of the media to a temperature below the ferroelectric Curie temperature of the ferroelectric layer. 
   
   
       23 . The method of  claim 22 , wherein the two directions comprise an up direction and a down direction, and further comprising, before or during step (c):
 if the measured built-in bias is more negative than the desired built-in bias, ensuring that the polarization of the at least a portion of the ferroelectric layer of the media is in the down direction; and   if the measured built-in bias is more positive than the desired built-in bias, ensuring that the polarization of the at least a portion of the ferroelectric layer of the media is the up direction.   
   
   
       24 . The method of  claim 22 , wherein step (c) comprises elevating the temperature of the at least a portion of the ferroelectric layer of the media to at least 200 degrees Celsius. 
   
   
       25 . The method of  claim 21 , wherein step (c) comprises elevating the temperature of the at least a portion of the ferroelectric layer of the media to a temperature equal to or above the ferroelectric Curie temperature of the ferroelectric layer. 
   
   
       26 . The method of  claim 25 , further comprising:
 (d) cooling the at least a portion of the ferroelectric layer of the media from the temperature equal to or above the ferroelectric Curie temperature to at least 50 degrees Celsius at a rate of at least 10 degrees per second or faster.   
   
   
       27 . The method of  claim 21 , wherein the at least a portion of the ferroelectric layer of the media is maintained at the elevated temperature for a length of time ranging between about 1 minute and about 100 minutes. 
   
   
       28 . The method of  claim 21 , wherein the at least a portion of the ferroelectric layer of the media is maintained at the elevated temperature for at least about 10 minutes. 
   
   
       29 . A method for adjusting a built-in bias of a media including a conductive layer and a ferroelectric layer above the conductive layer, the method comprising:
 (a) ensuring a polarization of at least a portion of the ferroelectric layer of the media to be in a same direction in which the built-in bias is to be moved; and   (b) elevating the temperature of the at least a portion of the ferroelectric layer of the media to a temperature that is below the ferroelectric Curie temperature of the media.   
   
   
       30 . The method of  claim 29 , wherein the built-in bias causes a preference for an up polarization or a down polarization, and wherein step (a) comprises:
 if the built-in bias is more negative than a desired built-in bias, ensuring that the polarization of the at least a portion of the ferroelectric layer of the media is in the down direction; and   if the built-in bias is more positive than the desired built-in bias, ensuring that the polarization of the at least a portion of the ferroelectric layer of the media is the up direction.   
   
   
       31 - 40 . (canceled)